Carrier treatment to improve catalytic performance of an ethylene oxide catalyst

ABSTRACT

A method for lowering the sodium content of different carriers which may have different physical properties as well as varying degrees of sodium is provided. The method, which lowers the sodium content from the surface, subsurface as well as the binding layer of the carrier, includes contacting a carrier with water. A rinse solution is recovered from the contacting. The rinse solution includes leached sodium from the carrier. The sodium content in the rinse solution is then determined. The contacting, recovering and determining are repeated until a steady state in the sodium content is achieved.

CROSS REFERENCE TO RELATED APPLICATION

The present invention claims the benefit of U.S. Provisional PatentApplication No. 61/824,108 filed May 16, 2013, the entire content anddisclosure of which is incorporated herein by reference.

FIELD OF THE DISCLOSURE

The present disclosure relates to improved carriers for a silver-basedethylene oxide catalyst, and more particularly, to a carrier treatmentprocess which lowers the sodium content of the carrier. The presentdisclosure also relates to a silver-based ethylene oxide catalyst thatincludes such a carrier and a process of producing ethylene oxide usingthe silver-based ethylene oxide catalyst.

BACKGROUND

As known in the art, high selectivity catalysts (HSCs) for theepoxidation of ethylene refer to those catalysts that possessselectivity values higher than high activity catalysts (HACs) used forthe same purpose. Both types of catalysts include silver as the activecatalytic component on a refractory support (i.e., carrier). Typically,one or more promoters are included in the catalyst to improve or adjustproperties of the catalyst, such as selectivity.

Generally, but not necessarily always, HSCs achieve the higherselectivity (typically 87 mole % or above) by incorporation of rhenium,and or an oxyanion of tungsten, molybdenum, or chromium as promoters.Typically, one or more additional promoters selected from alkali metals(e.g., lithium, potassium, and/or cesium), alkaline earth metals,transition metals (e.g., tungsten compounds), and main group metals(e.g., sulfur and/or halide compounds) are also included.

There are also ethylene epoxidation catalysts that may not possess theselectivity values typically associated with HSCs, though theselectivity values are improved over HACs. These types of catalysts canalso be considered within the class of HSCs, or alternatively, suchcatalysts can be considered to belong to a separate class, e.g., “mediumselectivity catalysts” or “MSCs.” These types of catalysts typicallyexhibit selectivities of at least 83 mole % and up to 87 mole %.

In contrast to HSCs and MSCs, the HACs are ethylene epoxidationcatalysts that generally do not include rhenium, and do not provide theselectivity values of HSCs or MSCs. Typically, HACs include cesium (Cs)as the main promoter.

It is well known that with extended use of a catalyst, the catalyst willshow signs of ageing (i.e., degraded performance) to a point until useof the catalyst is no longer practical. For obvious reasons, there is acontinuous effort to extend the useful lifetime (i.e., “longevity” or“usable life”) of the catalyst. The useful lifetime of the catalyst isdirectly dependent on the stability of the catalyst. As used herein, the“useful lifetime” is the time period for which a catalyst can be useduntil one or more of its functional parameters, such as selectivity oractivity, degrade to such a level that use of the catalyst becomesimpractical.

Stability of the catalyst has largely been attributed, in part, tovarious characteristics of the carrier. Some characteristics of thecarrier that have undergone much research include carrier formulation,surface area, porosity, particle morphology, and pore volumedistribution, among others.

The most widely used formulation for the carriers of ethyleneepoxidation catalysts are those based on alumina, typically α-alumina.Much research has been directed to investigating the effect of thealumina composition for improving stability and other properties of thecatalyst.

For example, the presence of sodium (Na) in an α-alumina carrier playsan important role in the ageing of an ethylene oxide catalyst. This factwas recognized for some time and several publications show evidence thatconfirmed the degrading effect of Na present on the surface of thecarrier. For instance, ISS analysis showed the increase of Na andchloride (Cl) on the surface as the catalyst ages. XPS data showed thatthe binding energy of both surface Na and Cl correspond to the formationof NaCl on the surface of the aged catalyst, Cl is adsorbed from the gasfeed. See, for example, the publications to G. Hoflund and D. Minahanentitled “Study of Cs-promoted α-alumina-supported silver, ethyleneepoxidation catalysts” Journal of Catalysis, 162, 1996, 48 and “Ion-beamcharacterization of alumina-supported silver catalysts used for ethyleneepoxidation” Nuclear Instruments and Methods in Physics Research SectionB: Beam Interactions with Materials and Atoms, 118, Issues 1-4, 1996,517. It was suggested in the aforementioned publications that Namigrates from the binder to the surface is accelerated by the drivingpotential provided by the surface chloride.

There are many publications which describe α-alumina carrier treatmentprocesses that are aimed at improving the catalytic performance, e.g.,stability of the resultant catalyst that is formed on the treatedcarrier. The processes generally wash the carrier prior to impregnatingthe carrier with silver and other promoters. The prior art treatmentprocesses are limited in scope in carrier treatments that deal generallywith removing Na from the surface of the carrier. For instance, bothU.S. Pat. Nos. 2,901,441 and 3,957,690 disclose a procedure for washinga carrier of a silver catalyst. In these publications, the α-aluminacarrier is washed by heating in a hot aqueous solution of organic acidand then rinsed with water. U.S. Pat. Nos. 5,102,848 and 5,504,053disclose washing of an α-alumina carrier using hot water. Similarly,U.S. Pat. No. 6,103,916 discloses washing of an α-alumina carrier for anethylene oxidation catalyst. In the '916 publication, washing is aimedto remove “leachable Na”. To test the carrier for its leachable Na, thewashed carrier is boiled in water and the resistivity of the drainedwater is more than 10,000Ω. Also, U.S. Pat. Nos. 6,368,998, 6,579,825,6,656,874, and 7,439,375 disclose a process of lowering a concentrationof ionizable species present on the surface of the carrier. Theionizable species, especially silicates, were extracted by boiling indeionized water. The process was repeated 3 times for 15 minutes, each.

By contrast, DE2933950 shows experimental evidence that soluble alkalimetal silicates are responsible for degrading the catalytic performance.The EP '950 publication discloses a process of washing the carrier witha hot NaOH solution to remove these salts and improve the catalyticperformance. Also, U.S. Pat. No. 6,846,774 discloses washing the aluminacarrier, of an ethylene oxide catalyst, with a hot aqueous basicsolution and maintaining the pH of the solution above 8.

Despite the numerous carrier treatments that are available to remove Nafrom the surface of a carrier, there remains a need in the art foradditional carrier treatment processes which provide furtherimprovements in the stability of an ethylene oxide catalyst. There is aparticular need for improving the stability of such catalysts byproviding a means to remove Na not only from the surface of the carrier,but from the subsurface and the binding layer of the carrier.

SUMMARY

In one embodiment, the present disclosure provides a means to lower thesurface and subsurface sodium content of a carrier as well as themajority of the sodium in the binding layer of the carrier. As such andin the washed carriers of the present disclosure, the migration ofsodium ions will be primarily limited to the more stable sodium withinthe bulk of the carrier. This migration will continue but it is,comparatively, rather slow in nature.

Specifically, the present disclosure provides a method for treatingdifferent carriers which may have different physical properties as wellas varying degrees of sodium contamination. In the method of the presentdisclosure, the carrier is rinsed with water. The carrier rinsingcontinues, or is repeated, even if the concentration of surface sodiumdrops to a conventionally low level. Actually that drop is intended tobe the initial phase of the rinsing process. The Na depleted surfacewill enhance the potential for faster sodium ion migration from thesubsurface of the carrier and from the binder's bulk, for furtherremoval.

The disclosure is different from the prior art by the fact that itrecognized that different commercial carriers may contain differentlevels of surface Na. Therefore, washing the carrier until the Na levelreached a certain level is an unreliable strategy. For all carriers, theNa depletion will start with a, relatively, higher level, and withcontinuous washing the rate of Na depletion will drop. This drop is anindication that the readily available surface Na is being exhausted andthe continuous washing is now removing the subsurface Na. The presentdisclosure teaches that the washing procedure should continue until asteady state of Na depletion is achieved.

The sodium removal efficiency is monitored using conventional methods,e.g., elemental analysis of the rinse solution or via measuring theelectrical conductivity of the rinsing solution. Deionized water is notan efficient medium for electrical conductivity. The extracted sodium inthe water, as well as the small amount of other dissolved ions, willcarry a current and provides a measurable electrical conductivity. Themagnitude of this conductivity will be a function of the concentrationof sodium. In the treatment process of the present disclosure, the rateof sodium removal continues to drop with each additional cycle ofrinsing. This is a sign that the surface sodium is depleted and theslower rate is a function of the slower diffusion of subsurface sodiumto the surface. With continual rinsing the sodium level in the risingsolution drops and accordingly the conductivity of the rinsing water,also, gradually drops, as a sign of depleted sodium from deeper zones ofthe carrier subsurface. This process continues until a steady state isachieved, i.e., when the amount of depleting sodium reaches, for allpractical purpose, a constant level. This indicates that all the surfaceand subsurface sodium has been virtually removed and additionaltreatment is not needed because it will only affect the bulk sodiumwhich is not expected to be totally removed.

The steady state is defined when at least three successive rinsingcycles result in removing the same level of sodium, as measured byanalysis, or by the electrical conductivity of the rinsing water. By“same level” is meant that the electrical conductivity of the three, ormore, successive rinsing cycles is within a value of ±0.5%.

In another embodiment of the present invention, the steady state can bedetermined when the slope of the change in conductivity of the rinsingwater is lower than 2 μSiemens/hour of treatment, preferably lower than1 μSiemens per hour of rinsing, and most preferably lower than 0.5μSiemens/hr of rinsing.

In one aspect of the present disclosure, a method of treating carriersis provided that lowers sodium content of the carrier. The methodincludes: contacting a carrier with water; recovering a rinse solutionfrom the contacting of the carrier with the water, the rinse solutioncomprises leached sodium from the carrier; determining sodium content inthe rinse solution; and repeating the contacting, recovering anddetermining until a steady state in the sodium content is achieved. Insome embodiments, the sodium content in the rinse solution can bedetermined by measuring the electrical conductivity of the rinsesolution.

In another aspect of the present disclosure, a process for producing anethylene oxide catalyst useful in the epoxidation of ethylene toethylene oxide is provided. This process comprises selecting a carrier;contacting the carrier with water; recovering a rinse solution from thecontacting of the carrier with the water, the rinse solution comprisesleached sodium from the carrier; determining sodium content in the rinsesolution, wherein the contacting, recovering and determining arerepeated until a steady state in the sodium content is achieved;depositing a catalytic effective amount of silver on the carrier; anddepositing a promoting amount of at least one promoter prior to,coincidentally with, or subsequent to the deposition of the catalyticeffective amount of silver.

In yet another aspect of the present disclosure, a method for the vaporphase conversion of ethylene to ethylene oxide in the presence of oxygenis provided. This method of the present disclosure comprises reacting areaction mixture comprising ethylene and oxygen in the presence of acatalyst that is prepared by: selecting a carrier; contacting thecarrier with water; recovering a rinse solution from the contacting ofthe carrier with the water, the rinse solution comprises leached sodiumfrom the carrier; determining sodium content in the rinse, wherein thecontacting, recovering and determining are repeated until a steady statein the sodium content is achieved; depositing a catalytic effectiveamount of silver on said carrier; and depositing a promoting amount ofat least one promoter prior to, coincidentally with, or subsequent tothe deposition of the catalytic effective amount of silver.

In yet a further aspect of the present disclosure, a carrier for asilver-based ethylene oxide catalyst is provided. The carrier of thepresent disclosure is characterized as having depleted Na from thesurface and near subsurface. A sign of the efficient depletion is whensuccessive water washing of the treated carrier yields, virtually, thesame amount of extracted sodium. This constant amount is generally inthe 5-20 ppm level, as measured by the residual sodium extraction test.The exact level of the residual sodium will vary, as a function of thecarrier composition, the concentration of sodium in the alpha aluminaand the binding material and the details of processing the carrierduring its manufacturing.

In yet a further aspect of the present disclosure, a silver-basedethylene oxide catalyst is provided. The catalyst of the presentdisclosure comprises a carrier having a steady state sodium content of20 ppm or less; a catalytic effective amount of silver; and promotingamount of at least one promoter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph of the rinse water conductivity (μSiemens/hr) vs. time(minutes, min.) for Carrier C in accordance with Example 3 of thepresent disclosure.

FIG. 2 is a graph of the rinse water conductivity (μSiemens/hr) vs. time(minutes, min.) for Carrier C in accordance with Example 3 of thepresent disclosure.

FIG. 3 is a graph of the rinse water conductivity (μSiemens/hr) vs. time(minutes, min.) for Carrier C in accordance with Example 4 of thepresent disclosure.

FIG. 4 is a graph of the rinse water conductivity (μSiemens/hr) vs. time(minutes, min.) for Carrier C in accordance with Example 4 of thepresent disclosure.

FIG. 5 is a graph of selectivity vs. time for Catalyst A and Catalyst Bthat are described in Example 5 of the present disclosure.

DETAILED DESCRIPTION

In one aspect, the present disclosure is directed to an improved carrierfor an ethylene epoxidation catalyst. The carrier is improved in that itimparts an enhanced stability to a silver-based catalyst derivedtherefrom. By ‘enhanced stability’ it is meant that the silver-basedcatalysts supported on the carrier of the present disclosure have longerusable lifetimes, and particularly, a significantly reduced degradationin selectivity as compared to such catalysts, impregnated on a prior artcarrier over equivalent time periods of usage.

The improved carrier is achieved by lowering the surface and subsurfacesodium content of a carrier as well as the sodium content in the bindinglayer. This lowering is achieved using successive rinsing with water ata defined temperature until a steady state in sodium content isachieved.

The carrier that can be employed in the present disclosure may beselected from a large number of solid supports which may be porous ornonporous. The carriers are relatively inert to the epoxidationfeedstock materials, products and reaction conditions for the intendeduse, such as for the epoxidation of an olefin. The carrier that can beemployed may be a refractory inorganic material such as, for example,alumina-, silica- or titania-based compounds, or combinations thereofsuch as alumina-silica carriers.

In one embodiment, the carrier is an alumina carrier. The aluminacarrier that can be employed in the present disclosure is composed ofany of the refractory alumina compositions known in the art for use inethylene oxidation catalysts. In one embodiment of the presentdisclosure, the carrier that is employed includes alpha-alumina as thealumina component. The alpha-alumina used in the present disclosuretypically has a high purity, i.e., about 80 weight % or more, and moretypically, 95 weight % or more alpha-alumina. Remaining components ofthe alumina carrier of the present disclosure may be other phases ofalumina, silica, mullite, alkali metal oxides and trace amounts of othermetal-containing and/or non-metal-containing additives or impurities.

When an alumina carrier is employed, the alumina carrier is typicallyporous and, in one embodiment, has a B.E.T. surface area of at most 20m²/g. In another embodiment, the B.E.T. surface area of the aluminacarrier is in the range from 0.1 m²/g to 10 m²/g. In yet anotherembodiment of the present disclosure, the alumina carrier that can beemployed in the present disclosure has a B.E.T. surface area from 0.2m²/g to 3 m²/g. In a further embodiment, the alumina carrier that can beemployed in the present disclosure is characterized by having a B.E.T.surface area from 0.3 m²/g to 3 m²/g, preferably from 0.5 m²/g to 2.5m²/g, and more preferably from 0.6 m²/g to 2.0 m²/g. The B.E.T. surfacearea described herein can be measured by any suitable method, but ismore preferably obtained by the method described in Brunauer, S., etal., J. Am. Chem. Soc., 60, 309-16 (1938).

In one embodiment, the alumina carrier that can be employed in thepresent disclosure has a water absorption value ranging from 0.2 cc/g to0.8 cc/g. In another embodiment, the alumina carrier that can beemployed in the present disclosure has a water absorption value rangingfrom 0.25 cc/g to 0.6 cc/g.

The alumina carrier that can be employed in the present disclosure canhave any suitable distribution of pore diameters. As used herein, the“pore diameter” is used interchangeably with “pore size”. In oneembodiment, the pore diameters are at least 0.01 microns (0.01 μm). Inanother embodiment, the pore diameters are at least 0.1 μm. In differentembodiments, the pore diameters can be at least 0.2 μm, or 0.3 μm.Typically, the pore diameters are no more than 50 μm.

The alumina carrier that can be employed in the present disclosure canbe monomodal or multimodal such as, for example, bimodal. Withoutwishing to be bound by any theory, it is believed that a catalyst with abimodal pore size distribution possesses a type of pore structure inwhich reaction chambers are separated by diffusion channels.

In one embodiment, at least 40% of the pore volume is attributable topores with diameters between 1 micrometer and 5 micrometers. In anotherembodiment, at least 60% of the pore volume is attributable to poreswith diameters between 1 micrometer and 5 micrometers. In yet a furtherembodiment, at least 80% of the pore volume is attributable to poreswith diameters between 1 micrometer and 5 micrometers.

In one embodiment, the median pore diameter of the carrier employed isbetween 1 micrometer and 5 micrometers. In another embodiment, themedian pore diameter of the carrier employed is between 1 micrometer and4.5 micrometers. In yet another embodiment, the median pore diameter ofthe carrier employed is between 1 micrometer and 4 micrometers. The porevolume from pores with a diameter of 5 micrometers and above istypically less than 0.20 ml/g, more typically less than 0.10 ml/g, andeven more typically less than 0.05 ml/g. The pore volume from pores witha diameter of 1 micrometer and less is typically less than 0.20 ml/g,and more typically less than 0.16 ml/g.

In some embodiments, the water pore volume of the alumina carrier can befrom 0.10 cc/g to 0.80 cc/g. In other embodiments, the water pore volumeof the alumina carrier can be from 0.20 cc/g to 0.60 cc/g. The porevolume and pore size distribution of the carrier described herein can bemeasured by any suitable method, but are more preferably obtained by theconventional mercury porosimeter method as described in, for example,Drake and Ritter, “Ind. Eng. Chem. Anal. Ed.,” 17, 787 (1945).

The carrier that can be employed in the present disclosure is preparedutilizing procedures well known in the art. Alternatively, the carrierthat can be employed in the present disclosure is commerciallyavailable. For example, suitable alumina carriers are manufactured andgenerally commercially available from Noritake of Nagoya, Japan, and theNorPro Company of Akron, Ohio.

In one embodiment and for example, an alumina carrier can be made bymixing a high-purity aluminum oxide, such as, for example,alpha-alumina, with temporary and permanent binders. The temporarybinders, that include burnout materials, are thermally decomposableorganic compounds of moderate to high molecular weight which, ondecomposition, enhance the pore structure of the carrier. The temporarybinders are essentially removed during firing when producing the finalcarrier. Some examples of burnout materials include cellulose,substituted celluloses, e.g., methylcellulose, ethylcellulose, andcarboxyethylcellulose, stearates (e.g., organic stearate esters, such asmethyl or ethyl stearate), waxes, granulated polyolefins (e.g.,polyethylene and polypropylene), walnut shell flour, and the like, whichare decomposable at the firing temperatures used in preparation of analumina carrier.

The permanent binders are typically inorganic clay-type materials havingfusion temperatures below that of the alumina, such as silica, aluminum,calcium or magnesium silicates with one or more alkali metal compounds.Optionally a transitional alumina can be present. The permanent binderstypically impart mechanical strength to the finished carrier.

After thorough dry-mixing, sufficient water and/or other suitable liquidis added to help form the mass into a paste-like substance. Carrierparticles are formed from the paste by conventional means, such asextrusion. After molding into the desired shape, the carrier particlescan be calcined at a temperature from 1200° C. to 1600° C. to form thesupport. When the particles are formed by extrusion, it may be desirableto also include extrusion aids. The amounts of extrusion aids requireddepend on a number of factors that relate to the equipment used. Suchfactors are well within the general knowledge of a person skilled in theart of extruding ceramic materials.

The carrier that can be employed in the present disclosure can be of anysuitable shape or morphology. For example, the carrier can be in theform of particles, chunks, pellets, rings, spheres, three-holes, wagonwheels, cross-partitioned hollow cylinders, and the like, of a sizepreferably suitable for employment in fixed bed reactors. In oneembodiment, the carrier particles typically have equivalent diameters inthe range of from 3 mm to 12 mm, and more typically in the range of from5 mm to 10 mm, which are usually compatible with the internal diameterof the tubular reactors in which the catalyst is placed. As known in theart, the term “equivalent diameter” is used to express the size of anirregularly-shaped object by expressing the size of the object in termsof the diameter of a sphere having the same volume as theirregularly-shaped object.

In some embodiments of the present disclosure, and prior to performingthe treatment step that lowers the surface and subsurface sodium contentof the carrier, the carrier can be treated by contacting or soaking thecarrier in a solution of an organic acid, an inorganic acid, a base, asalt, or combinations thereof. In one embodiment, a useful treatment isconducted by contacting or soaking the carrier in a solution of analkali hydroxide such as sodium hydroxide, potassium hydroxide, or anacid such as HNO₃. In one embodiment, the treating is conducted bycontacting or soaking the carrier in an aqueous solution of an alkalihydroxide, or HNO₃ at a concentration in the range of from 0.01 molar to10 molar. In another embodiment, the treating is conducted by contactingor soaking the carrier in an aqueous solution of an alkali hydroxide, orHNO₃ at a concentration in the range of from 0.05 molar to 5 molar.Useful contacting or soaking times typically range from 1 minute to 30days, with from 1 minute to 5 days being more typical, and with from 1minute to 1 day being even more typical. Useful solution temperaturestypically range from 0° C. to 250° C., with from 10° C. to 200° C. beingmore typically, and with from 20° C. to 150° C. being even more typical.After contacting or soaking, the support can be optionally dried byheating at a temperature from 80° C. to 500° C. Contacting or soakingcan be done at static conditions or with solution circulation. Thetreatment optionally may include contacting or soaking at onetemperature, usually higher, followed by contacting or soaking atdifferent temperature, usually lower. In one embodiment, the carrier iscontacted with sodium hydroxide prior to performing the treatment of thepresent disclosure that lowers the surface and subsurface Na content ofthe carrier.

The carrier that can be employed in the present disclosure typicallycontains a measurable level of sodium on the surface thereof. Theconcentration of sodium at the surface of the carrier will varydepending on the level of sodium within the different components of thecarrier as well as the details of its calcination. In one embodiment ofthe present disclosure, the carrier that can be employed in the presentdisclosure has a surface sodium content of from 5 ppm to 200 ppm,relative to the total mass of the carrier. In another embodiment of thepresent disclosure, the carrier that can be employed in the presentdisclosure has a surface sodium content of from 7 ppm to 70 ppm,relative to the total mass of the carrier. The sodium content mentionedabove represents that which is found at the surface of the carrier andthat which can be leached, i.e., removed, by water.

The surface sodium content of the carrier can be determined utilizing awater leachable test. In this test, the carrier is boiled in deionizedwater for 30 minutes. The ratio of water to carrier is typically 10:1 byweight. At the end of boiling process, the water is analyzed byInductive Coupled Plasma (ICP). The determined amount of Na is expressedin ppm relative to the total mass of the carrier sample.

Sodium will also be present in the subsurface of the carrier as well asin the bulk. By “subsurface” it is meant the portion of the carrier thatis positioned between the surface of the carrier and the bulk of thecarrier. Typically, the subsurface of the carrier is located a distanceof at most 100 nanometer inward from the surface of the carrier. By“bulk” it is meant the remaining portion of the carrier that is beneaththe subsurface of the carrier.

Sodium will also be present in the binding layer as well. The term“binding layer” denotes a layer of binding material that holds thealumina particles in place. In general, the binding layer will belocalized between the grain boundaries of the alpha alumina particles.In some embodiments, the binding layer may, partially, cover the surfaceof the carrier.

A treatment in accordance with the present disclosure is now performedon the carrier. Unlike prior art treatments that reduce the level ofsurface sodium from a carrier, the treatment of the present disclosurenot only lowers the surface sodium content of the carrier, but also thesubsurface sodium content and sodium content in the binding layer.

The treatment of the present disclosure includes contacting a carrierwith water. In one embodiment of the present disclosure, the water thatis used in this contact step has a temperature from 20° C. to 100° C. Inanother embodiment, the water employed in this contact step has atemperature from 50° C. to 95° C. In yet another embodiment, the wateremployed in this contact step is from 70° C. to 90° C. The temperatureof the water during the various stages of contacting can be the same ordifferent. The contact step can also be referred to herein as a rinsingstep since water is the only material used during the treatment step.The water that is employed is deionized or distilled water.

In one embodiment of the present disclosure, the carrier is treated insuccessive rinsing cycles, in a batch mode. The ratio of water tocarrier employed in this procedure is from 1:1 to 20:1. In anotherembodiment of the present disclosure, the ratio of water to carrieremployed in the aforementioned contacting is from 1.5:1 to 5:1. In yetanother embodiment of the present disclosure, the ratio of water tocarrier employed in the contacting is 2:1.

In the batch mode, water is added and circulated around a carrier for aperiod of time and thereafter the resultant rinse solution is recoveredand analyzed for sodium. In one embodiment, the period of time in whichthe water circulates around the carrier is from 5 minutes to 60 minutes.In another embodiment, the period of time in which the water circulatesaround the carrier is from 10 minutes to 40 minutes.

In other embodiments, a continuous mode is employed. In the continuousmode, water is trickled through a column containing a bed of a carrierat a flow rate which is sufficient to thoroughly wet the bed of thecarrier at all times. In the continuous mode, the rinse solution exitingthe column is continuously recovered and analyzed for sodium.

In either mode mentioned above, the recovered rinse solution is analyzedfor sodium content. In the batch mode, the analysis for sodium occursafter each successive rinsing step. In the continuous mode, the analysisfor sodium occurs continuously.

In one embodiment, the sodium content in the rinse solution isdetermined, for example, by measuring the electric conductivity thereofusing any suitable electrical conductivity meter. For example, theelectrical conductivity of the rinse solution can be performed using anOrion 3 Star Conductivity Bench-top Meter, provided with OrionConductivity Cell #013005MD, Electrode (manufactured by Thermo ElectronCorporation). In another embodiment, any other analytic method which canmeasure a sodium ion content in a rinsing solution can be used in thepresent disclosure.

As mentioned above, deionized water itself is not an efficient mediumfor electrical conductivity. Sodium ions in the deionized water willcarry a current and provide a measurable electrical conductivity. Themagnitude of this conductivity will be a function of the concentrationof sodium that has been leached from the carrier.

The contacting, recovering and analysis for sodium is repeated anynumber of times until a steady state in the sodium content is achieved.The term “steady state” is defined when three, or more, successiverinsing cycles result in removing the same level of sodium, as measuredby any of the aforementioned methods. In one embodiment, the steadystate is achieved after 4-25 successive rinsing cycles. In another, thesteady state is achieved after 5-15 successive rinsing cycles. In afurther embodiment, the steady state is achieved after 5-10 successiverinsing cycles. By “same level” is meant that the electricalconductivity of the three, or more successive rinsing cycles is within avalue of ±0.5%.

In another embodiment of the present invention, the steady state can bedetermined when the slope of the change in conductivity of the rinsingwater is lower than 2 μSiemens/hour of treatment, preferably lower than1 μSiemens per hour of rinsing, and most preferably lower than 0.5μSiemens/hr of rinsing.

After the aforementioned treatment, the concentration of sodium at thesurface of the carrier, which has achieved a steady state sodiumcontent, is 20 ppm or less. In another embodiment of the presentdisclosure and after performing the above treatment, the concentrationof sodium at the surface of the carrier, which has achieved a steadystate sodium content, is from 5 ppm to 15 ppm. The surface sodium ismeasured using the water leachable test mentioned above.

The carrier that is treated by the aforementioned treatment process hasa lower amount of surface sodium as compared to the same carrier priorto the treatment. In some embodiments, the reduction in surface sodiumcontent is 25% or greater. In another embodiments, the reduction insodium content is 50% or greater.

After reaching a steady state in sodium content, the treated carrier isdried. In one embodiment, the treated carrier is dried in oven. Inanother embodiment, the treated carrier is dried on a moving belt. Ineither embodiment, drying may be performed at a single temperature orvarious ramp and soak cycles can be used to dry the treated carrier. Inone embodiment, the treated carrier is dried at a temperature within arange from 100° C. to 300° C. In another embodiment, the treated carrieris dried at a temperature within a range from 120° C. to 200° C. Theduration of the drying may vary depending on the amount of carrier beingdried, and the conditions of the drying itself. In one embodiment, theduration of the drying step can be from 1 hour to 24 hours. Other timesthat are above and/or below the aforementioned range can also be used indrying the carrier.

In one embodiment, an ethylene epoxidation catalyst is produced from thetreated carrier described above. In order to produce the catalyst, atreated carrier having the above characteristics is then provided with acatalytically effective amount of silver thereon and/or therein. Thecatalysts are prepared by impregnating the treated carriers with silverions, compounds, complexes, and/or salts dissolved in a suitable solventsufficient to cause deposition of silver precursor compound onto and/orinto the carrier. The treated carrier can be impregnated with silver,along with any desired promoters, by any of the conventional methodsknown in the art, e.g., by excess solution impregnation, incipientwetness impregnation, spray coating, and the like. Typically, thecarrier material is placed in contact with a silver-containing solutionuntil a sufficient amount of the solution is absorbed by the carrier.Infusion of the silver-containing solution into the carrier can be aidedby application of a vacuum. A single impregnation or a series ofimpregnations, with or without intermediate drying, may be used,depending in part on the concentration of the silver component in thesolution. Impregnation procedures are described in, for example, U.S.Pat. Nos. 4,761,394, 4,766,105, 4,908,343, 5,057,481, 5,187,140,5,102,848, 5,011,807, 5,099,041 and 5,407,888, all of which areincorporated herein by reference. Known procedures for pre-deposition,co-deposition, and post-deposition of the various promoters can also beemployed.

Silver compounds useful for impregnation include, for example, silveroxalate, silver nitrate, silver oxide, silver carbonate, silvercarboxylate, silver citrate, silver phthalate, silver lactate, silverpropionate, silver butyrate and higher fatty acid salts and combinationsthereof. The silver solution used to impregnate the treated carrier cancontain any suitable solvent. The solvent can be, for example,water-based, organic-based, or a combination thereof. The solvent canhave any suitable degree of polarity, including highly polar, moderatelypolar or non-polar, or substantially or completely non-polar. Thesolvent typically has sufficient solvating power to solubilize thesolution components. A wide variety of complexing or solubilizing agentsmay be employed to solubilize silver to the desired concentration in theimpregnating medium. Useful complexing or solubilizing agents includeamines, ammonia, lactic acid and combinations thereof. For example, theamine can be an alkylene diamine having from 1 to 5 carbon atoms. In oneembodiment, the solution comprises an aqueous solution of silver oxalateand ethylene diamine. In some embodiments, the complexing/solubilizingagent may be present in the impregnating solution in an amount from 0.1to 10 moles of ethylene diamine per mole of silver. In otherembodiments, the complexing/solubilizing agent may be present in theimpregnating solution in an amount from 0.5 to 5 moles of ethylenediamine per mole of silver. In yet a further embodiment, thecomplexing/solubilizing agent may be present in the impregnatingsolution in an amount from 1 to 4 moles of ethylene diamine per mole ofsilver.

In one embodiment, the concentration of silver salt in the solution isin the range from 0.1% by weight to the maximum permitted by thesolubility of the particular silver salt in the solubilizing agentemployed. In another embodiment, the concentration of silver salt isfrom 0.5% to 45% by weight of silver. In yet another embodiment, theconcentration of silver salt is typically, from 5% to 35% by weight ofsilver.

Any one or more promoting species in a promoting amount can beincorporated into the treated carrier either prior to, coincidentallywith, or subsequent to the deposition of the silver. As used herein, a“promoting amount” of a certain component refers to an amount of thatcomponent that works effectively to provide an improvement in one ormore of the catalytic properties of a subsequently formed catalyst whencompared to a catalyst not containing said component. Examples ofcatalytic properties include, inter alia, operability (resistance torunaway), selectivity, activity, conversion, stability and yield. It isunderstood by one skilled in the art that one or more of the individualcatalytic properties may be enhanced by the “promoting amount” whileother catalytic properties may or may not be enhanced or may even bediminished. It is further understood that different catalytic propertiesmay be enhanced at different operating conditions. For example, acatalyst having enhanced selectivity at one set of operating conditionsmay be operated at a different set of conditions wherein the improvementis exhibited in the activity rather than in the selectivity.

For example, catalysts that are based on the treated carrier describedabove may include a promoting amount of an alkali metal or a mixture oftwo or more alkali metals. Suitable alkali metal promoters include, forexample, lithium, sodium, potassium, rubidium, cesium or combinationsthereof. In one embodiment, cesium can be employed. In anotherembodiment, combinations of cesium with other alkali metals can beemployed. The amount of alkali metal will typically range from 10 ppm to3000 ppm, more typically from 15 ppm to 2000 ppm, more typically from 20ppm to 1500 ppm, and even more typically from 50 ppm to 1000 ppm byweight of the total catalyst, expressed in terms of the alkali metal.

The catalyst that is based on treated carrier described above may alsoinclude a promoting amount of a Group IIA alkaline earth metal or amixture of two or more Group IIA alkaline earth metals. Suitablealkaline earth metal promoters include, for example, beryllium,magnesium, calcium, strontium, and barium or combinations thereof. Theamounts of alkaline earth metal promoters are used in similar amounts asthe alkali metal promoters described above.

The catalyst that is based on the treated carrier described above mayalso include a promoting amount of a main group element or a mixture oftwo or more main group elements. Suitable main group elements includeany of the elements in Groups IIIA (boron group) to VIIA (halogen group)of the Periodic Table of the Elements. For example, the treated carriercan include a promoting amount of one or more sulfur compounds, one ormore phosphorus compounds, one or more boron compounds, one or morehalogen-containing compounds, or combinations thereof. The treatedcarrier can also include a main group element, aside from the halogens,in its elemental form.

The catalyst that is based on the treated carrier described above mayalso include a promoting amount of a transition metal or a mixture oftwo or more transition metals. Suitable transition metals can include,for example, the elements from Groups IIIB (scandium group), IVB(titanium group), VB (vanadium group), VIB (chromium group), VIIB(manganese group), VIIIB (iron, cobalt, nickel groups), IB (coppergroup), and IIB (zinc group) of the Periodic Table of the Elements, aswell as combinations thereof. More typically, the transition metal is anearly transition metal, i.e., from Groups IIIB, IVB, VB or VIB, such as,for example, hafnium, yttrium, molybdenum, tungsten, rhenium, chromium,titanium, zirconium, vanadium, tantalum, niobium, or a combinationthereof.

In one embodiment, the one or more promoters comprise one or morespecies selected from Cs. K, or Li. In another embodiment, the promoterincludes Re and one or more species selected from Cs, K, Li, W, and S.In a further embodiment, the promoter includes Re and one or morespecies selected from Cs, Li, and S.

The catalyst that is based on the treated carrier described above mayalso include a promoting amount of a rare earth metal or a mixture oftwo or more rare earth metals. The rare earth metals include any of theelements having an atomic number of 57-103. Some examples of theseelements include lanthanum (La), cerium (Ce), and samarium (Sm).

The transition metal or rare earth metal promoters are typically presentin an amount of from 0.1 micromoles per gram to 10 micromoles per gram,more typically from 0.2 micromoles per gram to 5 micromoles per gram,and even more typically from 0.5 micromoles per gram to 4 micromoles pergram of total catalyst, expressed in terms of the metal.

All of these promoters, aside from the alkali metals, can be in anysuitable form, including, for example, as zerovalent metals or highervalent metal ions.

After impregnation with silver and any promoters, the impregnatedcarrier is removed from the solution and calcined for a time sufficientto reduce the silver component to metallic silver and to remove volatiledecomposition products from the silver-containing support. Thecalcination is typically accomplished by heating the impregnatedcarrier, preferably at a gradual rate, to a temperature in a range of200° C. to 600° C., more typically from 200° C. to 500° C., moretypically from 250° C. to 500° C., and more typically from 200° C. or300° C. to 450° C., at a reaction pressure in a range from 0.5 to 3 bar.In general, the higher the temperature, the shorter the requiredcalcination period. A wide range of heating periods have been describedin the art for the thermal treatment of impregnated supports. See, forexample, U.S. Pat. No. 3,563,914, which indicates heating for less than300 seconds, and U.S. Pat. No. 3,702,259, which discloses heating from 2to 8 hours at a temperature of from 100° C. to 375° C. to reduce thesilver salt in the catalyst. A continuous or step-wise heating programmay be used for this purpose.

During calcination, the impregnated carrier is typically exposed to agas atmosphere comprising air or an inert gas, such as nitrogen. Theinert gas may also include a reducing agent.

The impregnated catalysts described above can be used for the vaporphase production of ethylene oxide by conversion of ethylene to ethyleneoxide in the presence of oxygen. Generally, the ethylene oxideproduction process is conducted by continuously contacting anoxygen-containing gas with ethylene in the presence of the catalyst at atemperature in the range from 180° C. to 330° C., more typically from200° C. to 325° C., and more typically from 225° C. to 270° C., at apressure which may vary from about atmospheric pressure to 30atmospheres depending on the mass velocity and productivity desired. Atypical process for the oxidation of ethylene to ethylene oxidecomprises the vapor phase oxidation of ethylene with molecular oxygen inthe presence of the catalyst of the present disclosure in a fixed bed,tubular reactor. Conventional commercial fixed bed ethylene oxidereactors are typically in the form of a plurality of parallel elongatedtubes (in a suitable shell). In one embodiment, the tubes areapproximately 0.7 to 2.7 inches O.D. and 0.5 to 2.5 inches I.D. and15-45 feet long filled with catalyst.

The catalysts containing the impregnated carrier described above havebeen shown to be particularly selective catalysts in the oxidation ofethylene with molecular oxygen to ethylene oxide. Selectivity values ofat least 83 mol % up to 93 mol % are typically achieved. In someembodiments, the selectivity is from 87 mol % to 93 mole %. Theconditions for carrying out such an oxidation reaction in the presenceof the catalyst of the present disclosure broadly comprise thosedescribed in the prior art. This applies, for example, to suitabletemperatures, pressures, residence times, diluent materials (e.g.,nitrogen, carbon dioxide, steam, argon, and methane), the presence orabsence of moderating agents to control the catalytic action (e.g.,1,2-dichloroethane, vinyl chloride or ethyl chloride), the desirabilityof employing recycle operations or applying successive conversion indifferent reactors to increase the yields of ethylene oxide, and anyother special conditions which may be selected in processes forpreparing ethylene oxide.

In the production of ethylene oxide, reactant feed mixtures typicallycontain from 0.5 to 45% ethylene and from 3 to 15% oxygen, with thebalance comprising comparatively inert materials including suchsubstances as nitrogen, carbon dioxide, methane, ethane, argon and thelike. Only a portion of the ethylene is typically reacted per pass overthe catalyst. After separation of the desired ethylene oxide product andremoval of an appropriate purge stream and carbon dioxide to preventuncontrolled build up of inert products and/or by-products, unreactedmaterials are typically returned to the oxidation reactor. For purposesof illustration only, the following are conditions that are often usedin current commercial ethylene oxide reactor units: a gas hourly spacevelocity (GHSV) of 1500-10,000 h⁻¹, a reactor inlet pressure of 150-400psig, a coolant temperature of 180-315° C., an oxygen conversion levelof 10-60%, and an EO production (work rate) of 100-350 kg EO per cubicmeters of catalyst per hour. More typically, the feed composition at thereactor inlet comprises 1-40% ethylene, 3-12% oxygen, 0.3-40% CO₂, 0-3%ethane, 0.3-20 ppmv total concentration of organic chloride moderator,and the balance of the feed comprised of argon, methane, nitrogen, ormixtures thereof.

In other embodiments, the process of ethylene oxide production includesthe addition of oxidizing gases to the feed to increase the efficiencyof the process. For example, U.S. Pat. No. 5,112,795 discloses theaddition of 5 ppm of nitric oxide to a gas feed having the followinggeneral composition: 8 volume % oxygen, 30 volume % ethylene, about 5ppmw ethyl chloride, and the balance nitrogen.

The resulting ethylene oxide is separated and recovered from thereaction products using methods known in the art. The ethylene oxideprocess may include a gas recycle process wherein a portion orsubstantially all of the reactor effluent is readmitted to the reactorinlet after substantially removing the ethylene oxide product andbyproducts. In the recycle mode, carbon dioxide concentrations in thegas inlet to the reactor may be, for example, from 0.3 to 6, preferablyfrom 0.3 to 2.0, volume percent.

The following non-limiting examples serve to illustrate some aspects ofthe present disclosure. In these examples, a Method 1 or Method 2treatment, as described in greater detail herein below, was performed.The residual sodium content of the carrier before and after performingthe treatment was determined utilizing a water leachable test. In thistest, the carrier was boiled in deionized water for about 30 minutes.The ratio of water to carrier was 10:1 by weight. At the end of boilingprocess, the water was analyzed by Inductive Coupled Plasma (ICP).

Method 1 (Batch Mode): Hot water, 80° C., was added to an alpha-aluminacarrier at a ratio of 2:1. The water was circulated around the carrierfor 25 minutes and then drained for analysis. The electric conductivityof the drained water was measured at room temperature using Orion 3 StarConductivity Bench-top Meter, provided with Orion Conductivity Cell#013005MD, Electrode (manufactured by Thermo Electron Corporation).

An equal amount of fresh hot water was then added to the wet carrier andthe process was repeated for an additional rinsing cycle. The process ofdraining the used water and adding a fresh replacement was repeateduntil a steady state is reached.

The carrier was then dried in an oven at 150° C. for three hours.

Method 2 (Continuous Mode): The carrier was placed in a cylindricalvessel and hot deionized water, 90° C., trickled through the cylinder ata flow rate that was necessary for the carrier bed to be thoroughlywetted at all times. The drained water was continuously analyzed forsodium content, via an electrical conductivity meter as described abovein Method 1.

Example 1

Carrier A was treated using the batch mode, Method 1, in preparation forits use as a support for an ethylene oxide catalyst. Carrier A was anα-alumina carrier that had a surface area of 0.8 m²/g and its waterleachable Na was 60 ppm.

TABLE 1 Cycle # Conductivity of drained water 1 34.5 2 20.26 3 15.33 411.61 5 11.57 6 9.53 7 8.72 8 9.07

The treatment was considered complete because the last threeconductivity readings indicated that a steady state was reached. Thecarrier was then dried and its water leachable Na was 10 ppm.

Example 2

Carrier B was treated using Method 1, in preparation for its use as asupport for an ethylene oxide catalyst. Carrier B was an α-aluminacarrier that had a surface area of 0.7 m²/g and its water leachable Nawas 72 ppm.

TABLE 2 Cycle # Conductivity of drained water 1 112.4 2 52.4 3 36.3 430.2 5 22 6 21.04 7 18.79 8 18.45 9 14.2 10 13.2 11 12.7 12 12.4 13 12.5

The treatment was considered complete because the last threeconductivity readings indicated that a steady state was reached. Thecarrier was then dried and its water leachable Na was 14 ppm.

Example 3

Carrier C was treated using the continuous mode, Method 2, inpreparation for its use as a support for an ethylene oxide catalyst.Carrier C was an α-alumina carrier that had a surface area of 0.7 m²/gand its water leachable Na was 26 ppm. The carrier amount used was 130Kg and throughout the entire procedure the 90° C. water flow rate wasadjusted at 3 gallon/min. The conductivity of the rinsing water wasmeasured immediately as it exited the treatment vessel. The details ofthe procedure are illustrated in Table 3 and the data from the table areshown in FIGS. 1 and 2.

TABLE 3 Slope of decline in Slope of decline in Rinsing timeConductivity conductivity conductivity min μS μS/min μS/hour 0 15.3 0.084.8 10 12.1 20 11.3 30 10.2 40 9.1 50 8.4 0.029 1.74 60 7.9 70 7.5 807.1 90 6.8 100 6.5 110 6.1 120 5.8 130 5.8 140 5.6 150 5.7 160 5.50.0193 1.16 170 5.3 180 5.1 190 5 210 4.9 220 4.9 230 4.8 240 4.7 2504.6 260 4.5 270 4.4 0.01 0.6 280 4.3 290 4.3 300 4.2 310 4.2 0.005 0.3320 4.2 330 4.1

The treatment was considered complete because the slope of the change inconductivity of the rinsing water is lower than 0.5 μSiemens/hr. Thisindicated that a steady state was reached. The carrier was then driedand its water leachable Na was 12 ppm.

Example 4

Carrier C was treated using the continuous mode, Method 2, inpreparation for its use as a support for an ethylene oxide catalyst. Thecarrier amount used was 134 Kg and the throughout the entire procedurethe 90° C. water flow rate was adjusted at 6 gallon/min. Theconductivity of the rinsing water was measured immediately as it exitedthe treatment vessel. The details of the procedure are illustrated inTable 4 and the data from the table are shown FIGS. 3 and 4.

TABLE 4 Slope of decline in Slope of decline in Rinsing timeConductivity conductivity conductivity Min μS μS/min μS/hour 0 15.3 0.16 10 12.1 20 11.3 30 10.2 40 9.1 50 8.4 0.04 2.4 60 7.9 70 7.5 80 7.1 906.8 100 6.5 0.015 0.9 110 6.1 120 5.8 130 5.8 140 5.6 150 5.7 160 5.50.0119 0.7 170 5.3 180 5.1 190 5 210 4.9 220 4.9 0.01 0.6 230 4.8 2404.7 250 4.6 260 4.5 270 4.4 280 4.3 290 4.3 0.004 0.24 300 4.2 310 4.2320 4.2 330 4.1

The treatment was considered complete because the slope of the change inconductivity of the rinsing water is lower than 0.5 μSiemens/hr. Thisindicated that a steady state was reached. The carrier was then driedand its water leachable Na was 11 ppm.

Example 5

Stock Solution for Catalyst A: An 834 g portion of high purity silveroxide (Ames Goldsmith Corp.) was added to a stirred solution of 442 goxalic acid dehydrate (ACS Certified Reagent, Fisher) in about 2,800 gdeionized water. A precipitate of hydrated silver oxalate salt formed onmixing. Stirring was continued for 0.5 hours. The precipitate was thencollected on a filter and washed with deionized water. Analysis showedthat the precipitate contained 50.5 wt % silver. Next, 213.9 g of thesilver oxalate precipitate was dissolved in a mixture of 77.2 gramsethylenediamine (99+%, Aldrich) and 60.3 g deionized water. Thetemperature of the solution was kept below 40° C. by combining thereagents slowly, and by cooling the solution. After filtration, thesolution contained roughly 30 wt % silver, and had a specific gravity of1.52 g/mL.

Carrier for Catalyst A: For this catalyst, the carrier that was used,Carrier A, was treated in accordance with Example 1 of the presentdisclosure. Analysis of the treated carrier showed that the residualsodium value was 10 ppm.

Catalyst A Preparation

Silver based catalyst preparation and activation followed generallyconventional procedures, as disclosed above. Specifically, a 300 gportion of the alumina support was placed in a flask and evacuated toabout 0.1 torr prior to impregnation. To the above silver solution wereadded aqueous solutions of cesium hydroxide, perrhenic acid, andammonium sulfate in order to prepare a catalyst composition according toexamples 5-10 of U.S. Pat. No. 4,766,105 to Lauritzen et al. Afterthorough mixing, the promoted silver solution was aspirated into theevacuated flask to cover the carrier while maintaining the pressure atabout 0.1 torr. The vacuum was released after about 5 minutes to restoreambient pressure, hastening complete penetration of the solution intothe pores. Subsequently, the excess impregnation solution was drainedfrom the impregnated carrier.

Calcination of the wet catalyst was performed on a moving belt calciner.In this unit, the wet catalyst was transported on a stainless steel beltthrough a multi-zone furnace. All zones of the furnace were continuouslypurged with pre-heated, nitrogen and the temperature was increasedgradually as the catalyst passed from one zone to the next. The heatsupplied to the catalyst was radiated from the furnace walls and fromthe preheated nitrogen. In this example, the wet catalyst entered thefurnace at ambient temperature. The temperature was then increasedgradually to a maximum of about 450° C. as the catalyst passed throughthe heated zones. In the last (cooling) zone, the temperature of the nowcalcined catalyst was immediately lowered to less than 100° C. before itemerged into ambient atmosphere. The total residence time in the furnacewas approximately 45 minutes.

Catalyst B, a high selectivity catalyst was prepared using the samecarrier and same impregnating solution as used in catalyst A. The onlyexception is that the carrier was washed using a limited washingprotocol such as typically employed in the prior art in which asteady-state conductivity was not meant. Analysis of the treated carriershowed that the residual sodium value was 26 ppm.

The two catalysts were tested under stressful conditions of work rateand gas composition in order to accelerate their ageing. The decline inselectivity of the two catalysts demonstrate that the catalyst that wasprepared using a carrier as treated using the method of the presentdisclosure is more stable. This is shown, for example, in the FIG. 5.

While the present disclosure has been particularly shown and describedwith respect to various embodiments thereof, it will be understood bythose skilled in the art that the foregoing and other changes in formsand details may be made without departing from the spirit and scope ofthe present disclosure. It is therefore intended that the presentdisclosure not be limited to the exact forms and details described andillustrated, but fall within the scope of the appended claims.

What is claimed is:
 1. A method of lowering sodium content of a carrier,said method comprising: contacting a carrier with water; recovering arinse solution from the contacting of the carrier with said water, saidrinse solution comprises leached sodium from said carrier; determiningsodium content in the rinse solution; and repeating the contacting,recovering and determining until a steady state in the sodium content isachieved.
 2. The method of claim 1, wherein the sodium content in therinse solution is determined by measuring electrical conductivity of therinse solution.
 3. The method of claim 1, wherein said carrier comprisesalumina.
 4. The method of claim 1, wherein said water has a temperaturefrom 20° C. to 100° C.
 5. The method of claim 1, wherein said water hasa temperature from 70° C. to 90° C.
 6. The method of claim 1, whereinsaid contacting includes a water to carrier ratio from 1:1 to 20:1. 7.The method of claim 1, wherein said contacting includes a water tocarrier ratio of 2:1.
 8. The method of claim 1, wherein said contacting,recovering and determining is performed in a batch mode and said steadystate is achieved when analysis of the sodium content of at least threesuccessive rinse solutions vary in a value within ±0.5%.
 9. The methodof claim 2, wherein said contacting, recovering and determining isperformed in a batch mode and said steady state is achieved when theelectrical conductivity of at least three determinations is within avalue of ±0.5%.
 10. The method of claim 1, wherein said contacting,recovering and determining is performed in a batch mode batch mode, saidbatch mode comprises circulating said water around said carrier.
 11. Themethod of claim 1, wherein said contacting, recovering and determiningis performed in a continuous mode and said steady state is achieved whena slope of a change of electrical conductivity of the rinsing solutionis lower than 0.2 μSiemens/hour.
 12. The method of claim 11, whereinsaid continuous mode comprises trickling said water through a columncontaining a bed of said carrier at a flow rate to continuously wet thebed of said carrier.
 13. The method of claim 1, wherein said carrier hasa residual sodium content of from 4 ppm 200 ppm prior to performing saidcontacting.
 14. The method of claim 1, wherein said carrier has asurface sodium content of 20 ppm or less after reaching said steadystate.
 15. The method of claim 1, wherein said leached sodium is from asurface, subsurface and a binding layer of said carrier.
 16. A processfor producing an ethylene oxide catalyst useful in the epoxidation ofethylene to ethylene oxide, comprising: selecting a carrier; contactingsaid carrier with water; recovering a rinse solution from the contactingof the carrier with said water, said rinse solution comprises leachedsodium from said carrier; determining sodium content in the rinsesolution, wherein said contacting, recovering and determining arerepeated until a steady state in sodium content in the rinse solution isachieved; depositing a catalytic effective amount of silver on saidcarrier; and depositing a promoting amount of at least one promoterprior to, coincidentally with, or subsequent to the deposition of thecatalytic effective amount of silver.
 17. The process of claim 16,wherein the sodium content in the rinse solution is determined bymeasuring electrical conductivity of the rinse solution.
 18. The processof claim 16, wherein said at least one promoter is selected from analkali metal, a Group IIA alkaline earth metal, a transition metal, arare earth metal, sulfur, boron, phosphorus, and a halogen.
 19. Theprocess of claim 16, wherein said at least one promoter comprises atleast cesium lithium, and rhenium.
 20. The process of claim 16, whereinsaid at least one promoter comprises at least potassium.
 21. The processof claim 19, further comprising sulfur, tungsten or a combination ofsulfur and tungsten.
 22. The process of claim 16, wherein saidcontacting, recovering and determining is performed in a batch mode andsaid steady state is achieved when analysis of the sodium content of atleast three successive rinse solutions vary in a value within ±0.5%. 23.The process of claim 17, wherein said contacting, recovering anddetermining is performed in a batch mode and said steady state isachieved when the electrical conductivity of at least threedeterminations is within a value of ±0.5%.
 24. The process of claim 16,wherein said contacting, recovering and determining is performed in abatch mode batch mode, said batch mode comprises circulating said wateraround said carrier.
 25. The process of claim 16, wherein saidcontacting, recovering and determining is performed in a continuous modeand said steady state is achieved when a slope of a change of electricalconductivity of the rinsing solution is lower than 0.2 μSiemens/hour.26. The process of claim 25, wherein said continuous mode comprisestrickling said water through a column containing a bed of said carrierat a flow rate to continuously wet the bed of said carrier.
 27. A methodfor the vapor phase conversion of ethylene to ethylene oxide in thepresence of oxygen, said method comprising reacting a reaction mixturecomprising ethylene and oxygen in the present of a catalyst, saidcatalyst is prepared by: selecting a carrier; contacting said carrierwith water; recovering a rinse solution from the contacting of thecarrier with said water, said rinse solution comprises leached sodiumfrom said carrier; determining sodium content in the rinse solution,wherein said contacting, recovering and determining are repeated until asteady state in the sodium content is achieved; depositing a catalyticeffective amount of silver on said carrier; and depositing a promotingamount of at least one promoter prior to, coincidentally with, orsubsequent to the deposition of the catalytic effective amount ofsilver.
 28. The method of claim 27, wherein the sodium content in therinse solution is determined by measuring electrical conductivity of therinse solution.
 29. The method of claim 27, wherein said at least onepromoter is selected from an alkali metal, a Group IIA alkaline earthmetal, a transition metal, a rare earth metal, sulfur, phosphorus,boron, and a halogen.
 30. The method of claim 27, wherein said at leastone promoter comprises at least cesium lithium, and rhenium.
 31. Themethod of claim 30, further comprising sulfur, tungsten or a combinationof sulfur and tungsten.
 32. The method of claim 27, wherein saidcontacting, recovering and determining is performed in a batch mode andsaid steady state is achieved when analysis of the sodium content of atleast three successive rinse solutions vary in a value within ±0.5%. 33.The method of claim 28, wherein said contacting, recovering anddetermining is performed in a batch mode and said steady state isachieved when the electrical conductivity of at least threedeterminations is within a value of ±0.5%.
 34. The method of claim 27,wherein said contacting, recovering and determining is performed in abatch mode batch mode, said batch mode comprises circulating said wateraround said carrier.
 35. The method of claim 27, wherein saidcontacting, recovering and determining is performed in a continuous modeand said steady state is achieved when a slope of a change of electricalconductivity of the rinsing solution is lower than 0.2 μSiemens/hour.36. The method of claim 35, wherein said continuous mode comprisestrickling said water through a column containing of bed of said carrierat a flow rate to wet the bed of said carrier.
 37. A method of loweringsodium content of carrier comprising washing a carrier in deionizedwater until a steady state of sodium content is achieved.
 38. A carrierfor a silver-based ethylene oxide catalyst, said carrier having a steadystate sodium content of 20 ppm or less.
 39. A silver-based ethyleneoxide catalyst comprising: a carrier having a steady state sodiumcontent of 20 ppm or less; a catalytic effective amount of silver; and apromoting amount of at least one promoter.